The invention pertains to the general field of loudspeakers and more particularly to improvements and modifications to an electrolytic loudspeaker assembly as disclosed in U.S. Pat. No. 5,392,358 which is assigned to MZX Corporation which is also the applicant of the instant application.
From the beginning of xe2x80x9chigh fidelityxe2x80x9d audio systems, engineers have endeavored to develop loudspeakers that were relatively free from distortion and that had a frequency response which would allow all types of music from the simple to the intricate to be closely reproduced. Loudspeakers are categorized as being either magnetic, moving coil speakers or non-magnetic, electrostatic speakers/transducers. Due to the fact that the instant invention is categorized as electrostatic, this background art will focus on these types of loudspeakers.
Most conventional electrostatic speakers consist of a flexible center membrane or diaphragm having on each side a fixed electrode designed in the shape of a grid of wire. The wires are placed apart thereby enabling sound waves, which are generated by the movement of the flexible membrane, to be emitted. The wires are held within a dielectric insulation material and the flexible membrane is coated with a highly resistive material. The membrane is further suspended within an open-latticed frame between the electrode wires 50 that when operated, relatively small segments of the diaphragm vibrate as a result of the electrostatic fields acting upon the diaphragm.
Electrostatic transducer loudspeakers are considered to be superior in many respects over the moving-coil type of speakers. However they have received generally poor acceptance. This poor acceptance is a result of the mechanical complexity of some designs, low acoustic output, the requirement for a comparatively large radiating area, and a dependence upon the application of a relatively high d-c polarizing bias voltage between the flexible diaphragm and the wire grid electrodes. For example, a typical full range push-pull electrostatic speaker requires a bias voltage of 3500 volts d-c and a driving amplifier with a power capacity of from 60 to 100 watts. Additionally, electrostatic speakers are only able to capable reproduce the mid-range and higher audible frequencies. As a result of this it is usually necessary to utilize a bass speaker, which can be connected to the loudspeaker assembly or be a separate module, such as a sub-woofer.
To alleviate some of the above problems, transducers utilizing electrets as the diaphragm have been utilized. The electret diaphragm was thought to be permanently polarized or charged and therefore did not require a separate polarizing d-c voltage. However, these electrets have been found to be unsatisfactory for application as loudspeakers because they decay, at least to a first approximation, because the misalignment of the partially oriented dipoles is a random process.
A search of the prior art did not disclose any patents that read directly on the claims of the instant invention however the following U.S. patents were considered related:
The U.S. Pat No. 5,3?9,358 Driver patent discloses an improved electrolytic loudspeaker assembly that is designed to reproduce a broad band of audio signals. The loudspeaker assembly consists of a thin, non-magnetic capacitive transducer and a transducer driver unit. The transducer consists of a compound diaphragm further consisting of a vibratory center section having attached to each of its surfaces a respective front section and a back action. All three sections of the compound diaphragms are held captive by a frame assembly. The transducer is driven and controlled by the transducer driver unit which couples the audio signal to the transducer""s front and back sections and supplies an unregulated, d-c bias voltage to the transducers center section.
The U.S. Pat. No. 4,160,882 Driver patent discloses an electrostatic transducer that functions as a loudspeaker. The transducer consists of two parallel diaphragms each consisting of two plastic sheets, having different charge carrying characteristics, that are sandwiched between an electrically conductive layer. The two diaphragms are separated by a centrally located perforated electrically conductive sheet and a dielectric material sandwiched between the conductive sheet and each diaphragm. The diaphragm""s two electrically conductive layers are connected across the secondary winding of an audio transformer and the centered electrically conductive sheet is connected to the center tap of the transformer. Thus, when the transformer applied an audio signal the two diaphragms are driven in a push-pull relation to reproduce the audio.
The U.S. Pat. No. 3,942,0109 Kawakami et al patent discloses an electrostatic transducer that can be utilized as either a speaker or microphone. The transducer consists of a vibrating plate or electret diaphragm having a monocharge of positive or negative potential on its surface. The electret diaphragm is made of a thin polymer film that bonded to a support so that uniform tension exits. A pair of electrically conductive electrodes are brought in contact with opposite sides of the polymer films, arid an eletrostatic shield, such as a mesh, covers the surface of the two electrodes. A d-c voltage is time applied across the electrodes to allow the electret to heat to its curie temperature of 120xc2x0 C. The electret is subsequently cooled to produce a quasi permanent state of electric polarization.
The U.S. Pat No. 3,705,312 electric patent discloses a method for preparing a thin-film electret. The method includes placing a thin polymer film between two electrodes together with a dielectric plate. A voltage of about 30 kev is then applied across the resulting sandwich of elements for about one minute at room temperature and at atmospheric pressure. The method Produces charge-densities which are greater by a factor of three than those previously reported.
The U.S. Pat No. 3,345,469 Rod patent discloses a loudspeaker that operates on electrostatic principles. The speaker consists of a centrally located movable diaphragm which is coated on both sides with a thin, flexible eletrically conductive layer. On each side of the diaphragm is located at least one hermetically sealed plastic dielectric sheet. When air or other gas is trapped between the sheets and the diaphragm, a buffer zone is created. To each outer-most dielectric sheet is attached an electrode and to the centered conductive diaphragm is likewise attached an electrode. The two buffer electrodes are connected across the secondary winding of a step-up transformer and the diaphragm electrode is connected through a d-c voltage source to the centertap of the transformer. The transformer""s primary winding is connected to the diaphragm driving signal that is derived from the signal input from a conventional low-impedance amplifier.
The improvements and modifications disclosed herein enhance the performance of the electrolytic loudspeaker assembly to better reproduce a broad band of the audible spectrum. The improvements and modifications further allow the loudspeaker assembly to maintain its relatively flat, non-magnetic and non-ferrous structure. Because of this flat structure the inventive electrolytic loudspeaker assembly can be placed or mounted in places that are normally unsuitable for conventional loudspeakers. The flattened design also allows the structure to be bent or curved, which further extends its mounting capabilities in locations such as a curved corner or to items such as a lamp shade. Additionally, as a result of its inherent low weight, the loudspeaker assembly is ideal for use in weight-critical environments such as in aircraft and spacecraft.
In its most basic design configuration, the electrolytic loudspeaker assembly consists of:
A. a capacitive transducer consisting of:
a) a compound diaphragm further consisting of:
(1) A center section having a first side and a second side. Attached to the first side is a front section and attached to the second side is a rear section,
(2) A center electrode which is in electrical contact with the center section, a front electrode which is in electrical contact with the front section, and a rear electrode which is in electrical contact with the rear section,
b) a frame assembly consisting of:
(1) A front section having an inner surface and an outer surface,
(2) A rear Section having an inner surface and an outer surface. Between the two inner surfaces is suspended the compound diaphragm,
B. A transducer driver unit which interfaces with the compound diaphragm by means of the center, front and rear electrodes. The driver unit is designed to accept an incoming audio signal and to produce an alternating signal, analogous to the incoming audio signal, which drives the compound diaphragm.
The improvements to the center section, which functions as the primary vibratory element, are disclosed in two design configurations, each of which include the center electrode which attache to the transducer driver unit. The front and back sections, which attach to the respective sides of the center section, are disclosed in three design configurations. Each section includes a front and rear electrode respectively which are also attached to the transducer driver unit. Likewise, the frame assembly which encloses the compound diaphragm to form the capacitive transducer is disclosed in three design configurations.
The capacitive transducer, in electrical terms, resembles a pair of double anode diodes connected in series or a unijunction transistor. The compound diaphragm of the capacitive transducer is driven and controlled by the transducer driver unit which is disclosed in two design configurations.
In view of the above disclosure, it is the primary object of the invention to add improvements and to provide modifications which enhance the performance of the basic electrolytic loudspeaker assembly. It is also an object of the invention to provide an electrolytic loudspeaker assembly that:
is highly reliable and easily maintained,
can be designed to fit in a particular space requirement,
does not require the high signal and bias voltage needed to operate conventional electrostatic speakers,
can be mounted in various positions and locations that are not possible with current magnetic moving-coil speakers and electrostatic speakers, and
is cost effective from both a consumer""s and manufacturer""s point of view.
These and other objects and advantages of the present invention will become apparent from the subsequent detailed description of the preferred embodiment and the claims taken in conjunction with the accompanying drawings.